The long range goal of the proposed research is to further our understanding of how the brain uses sensory information to guide body movements. To study this problem we have chosen the vestibular-neck reflex, which acts to stabilize the head on the body trunk. This reflex is understandably more complex than the well-understood vestibulo-ocular reflex that controls the eyes, but is a simpler sensory-motor system than the ones involved in general control of the limbs. Our approach is to extend to the vestibular-neck reflex the techniques of analysis of timing (dynamics) and spatial properties (3-dimensional directionality) that have been successfully applied to understanding vestibulo-ocular responses. The proposed experiments are directed toward three specific aims: 1. We will determine the relative contributions to the vestibular-neck reflex of the two vestibular signals relayed from the inner ear, the head rotation velocity signal carried by semicircular canal fibers and the head position or linear acceleration signal carried by the fibers from the otolithic maculae of the utricle and saccule. We expect canal signals to dominate for rapid motions and otolith signals to dominate for slower motions, with both the dynamics and spatial properties to differ for otolith versus canal signals, reflecting the different behavioral problems and mechanical loads faced for slow versus rapid head motions. 2. We will test the spatial properties and dynamics of otolith and canal components of the vestibular-neck reflex for the effects of factors such as a) sensory and motor deficits produced by plugging semicircular canals or selectively disabling major neck muscles, b) changes in head tilt with respect to gravity, and the posture of the head with respect to the body, and c) inactivation of the cerebellum. We expect to see greater adaptability and more pronounced context- specific responses for the vestibular-neck reflex than have been seen for the vestibulo-ocular reflex. 3. We will distinguish otolith and canal signals carried by vestibular- cervical neurons and explore the role of vestibular-cervical neurons in vestibular-neck reflex spatial properties, dynamics, and responses to factors listed above that affect the vestibular-neck reflex. We expect to find neurons that carry purely sensory signals and other neurons that carry adaptable or context-specific responses. We will test neurons for cerebellar input to see whether the cerebellum selectively influences neurons with adaptable and context-specific responses. We hope this research will expand our knowledge of sensory-motor neural systems. The results may ultimately be relevant to treatment of neurological or neuromuscular disease such as torticollis and oculomotor disorders, or neurological injury in general.